{
  interface PersonFather {
    age: number;
    sex: string;
  }
  
  interface Teacher extends PersonFather {
    level: string;
    subject: string;
  }
  
  let lee: Teacher = {
    age: 23,
    sex: '女',
    level: 'middle',
    subject: '数学'
  };
}

{
  let lee = {
    age: 23,
    sex: '女',
    level: 'middle',
    subject: '数学'
  };
  // 类型推导，这样lee对象添加或者删除属性，ts可以自动检测出来
  type Te = typeof lee;
  // 类型推到的灵活应用
  function LeeSon(): Te {
    return {
      age: 23,
      sex: '女',
      level: 'middle',
      subject: '数学'
    }
  }
}